The lesson presented here has 23 as seen in lesson 7. But the introduction text mentions 21. So what is the correct number?

The vowel we are talking about is called dependent vowels. These vowels have to be combined with a consonant to form a syllable or word. They cannot be by itself. On the contrary, the independent vowels can be used by itself and it does not need to combine with a consonant.

The official number of dependent vowel mentioned in the official dictionary is 21. The last 3 vowels we presented in the lesson are considered to be a combination of vowels. This make the total number of vowels taught here to be 20. The vowel that is not taught in the lesson the inherit vowel. This vowel is called SRAK OR (AQ). Every consonant stands by itself is considered to be combined with this vowel. This make the count to be 21.

If we count all of the different combination of vowels, we would have 7 (4 of which we covered in our lessons). This makes our total number of vowels to be 28. These 7 vowels are: (need Khmer Unicode to see the characters below)